1. Technical Field
The present invention relates to a drive system for curved segments of roller conveyors, and more specifically to cost-effective, efficient, and reliable systems of transferring power from a straight segment to an adjacent curved segment of an accumulator conveyor system.
2. Related Art
Roller conveyors are commonly found in a variety of a manufacturing, distribution, and warehouse facilities. Most roller conveyor systems include a variety of straight and curved segments configured to allow products, individually or packaged together, to wind their way through a facility past various operations and to various destinations. An exemplary roller conveyor is an accumulation conveyor configured to allow live storage of products or loads on the conveyor system. Accumulator conveyors are configured to start and stop various segments or portions of segments as needed, to allow the packages or loads to accumulate or be conveyed along to a destination.
Most roller conveyor systems typically include a supporting structure having frames that extend along the path of travel and a plurality of rollers extending between the frames, at right angles to the direction of travel. A drive system transfers power to the individual rollers on which the loads rest. The drive system causes the rollers to spin and the load is conveyed to its desired destination.
The curved segments of roller conveyors and in particular, the drive system for curved segments is traditionally more complex, difficult, and expensive than drive systems for similar straight segments. A drive system for any segment, whether straight or curved, must allow smooth transitions between being engaged and disengaged, allow loads to travel smoothly, and provide efficient, reliable, low maintenance, and effective transfer of power to the individual rollers whether in transportation mode or accumulation. In the curved segments, it is particularly difficult to have the rollers in the curved segment to accumulate in sequence with the straight conveyor it is feeding because the drive system for the curved conveyor segment is required to be of a different or additional drive system than the adjacent straight conveyor segment. The drive system for curved segments in prior art systems employ complex electronic clutches, sophisticated pneumatic circuits or expensive motorized roller solutions that drop the drive off the curved segment in sequence with the adjacent straight conveyor.
In contradistinction to curved segments, many manufactures of roller conveyors have developed cost-effective, efficient, and reliable drive systems for straight segment roller conveyors. More specifically, most manufacturers now use an elongated, substantially flat, wide belt running the entire length of the straight segment to drive the rollers. This elongated drive belt is located on the opposing sides of the rollers from the load surface and is substantially wider than V-belts. As the belt is not as wide as the rollers, it is typically positioned on one side of the straight conveyor segment, although it may be positioned anywhere between the frames so long as it is capable of engaging the rollers. If used in an accumulation conveyor system, the drive system may be split into various segments such that it is configured to engage or disengage at various zones depending if it is desirable for the loads to be stationary or moving in those zones. Therefore, a single, straight conveyor segment may have multiple zones where loads may be selectively transported or accumulated as desired.
The use of a flat, elongated, and wide belt has specific advantages if a roller stops turning, such as when loads jam and cause the rollers to stop spinning. If the roller stops rotating, the frictional load and associated heat load of the belt slipping against the roller(s) is spread over a large section of the belt, thereby minimizing wear on the drive belt. This type of drive system using an elongated wide belt is a substantial improvement over prior systems that used complicated drive shafts, power rollers or V-belts, which typically powered only selected rollers, such that drive from the selected rollers must be transferred to the adjacent rollers using inefficient O-rings that are set within the surface of the individual rollers. One major issue with using O-rings to power adjacent rollers is that they are not an efficient transfer of power, and typically only two to three and at most, four to six adjacent rollers may be powered before the system is incapable of efficiently transferring the loads. In addition, V-belts and O-rings quickly wear out due to the frictional load, especially if a roller stops rotating for any reason. Therefore, manufacturers have avoided any roller to roller power transfer, other than for one to two adjacent rollers.
While cost-effective, long lasting, reliable, and efficient drive systems have been developed for straight segments of roller conveyers, there is still room for improvement of drive systems used in curved segments of conveyor systems, in particular when they are used in conjunction with an accumulation conveyor. Due to the radius of the curved section, it is impracticable if not impossible to use on curved segments the above described elongated, wide, and flat belt that is used on straight segments. As illustrated in FIGS. 1-4, a variety of expensive and less efficient drive systems have been proposed to provide drive to the individual rollers on a curved roller conveyor segment. When the curved roller conveyor segment is used in an accumulation conveyor, where it is desirable to start and stop the curved segments independent of other sections, special expensive mechanisms must be used such as a separate motor to drive the curved segment or clutches to selectively transfer power from the straight segment to the curved segment.
One such prior art curved segment is illustrated in FIG. 1 and has its own independent motor and an elongated continuous V-belt with various drive pulleys on each roller and additional tension rollers attached to the frame. The first downside to the system illustrated in FIG. 1 is that it requires an independent motor, which is expensive and increases the product cost. Installation costs are also increased as power must be run to each motor location. Conveyor systems requiring a separate motor and therefore separate electric power connections are more difficult to reconfigure due to the requirement for moving the electric motor and associated power connections. In addition, the elongated continuous V-belts are typically expensive as changes in radius, length, and degree of curve all change the length of the required belt which may in turn require the system to use numerous custom sized belts. Another problem is that the curve of the conveyor segment may create additional wear on the continuous V-belt by each pulley, as each pulley has an axis that is not aligned with adjacent pulleys. Another downside to using a continuous V-belt on a curved section is that if a roller or rollers stop turning, it may cause the V-belt to also stop, while the motor and associated drive pulley continue spinning, creating localized wear and heat, which significantly shortens the life of the V-belt.
In regards to FIG. 2, some manufactures, to avoid issues with separate motors for curved segments have proposed drive shafts with universal joints and individual drive rollers frictionally engaging at least some of the load bearing rollers, all of which significantly increase product cost and are difficult to and expensive to maintain. In some instances, a complicated system having a transfer belt and short curved drive belt segments are used. The curved drive belt must typically be customized to the application and specific design requirements and changes in the radius or length require different belts, a change in the number of required belts or a change in underlying belt supports. These customized belts may cause difficulty for the operators of the conveyor system in ordering the proper belt in the correct radius and length as well are difficult to install properly so they track as desired. The drive shafts, universal joints, customized belts, and secondary friction drive rollers all create a very expensive drive system as well as increased installation costs.
Other manufacturers, as illustrated in FIGS. 3 and 4 in the curved segments, may use an extremely long V-belt to transfer power from a straight segment or a motor driving the straight segment. Although not illustrated, some systems use a V-belt similar to that illustrated in FIG. 3 with a transfer pulley and clutch allowing drive to be transferred from the straight segment without the use of the illustrated motor. The long V-belts may experience many of the problems listed above.
All of the above illustrated systems include drawbacks that reduce the reliability, longevity, or increase the cost of the drive system for the curved conveyor segments as well as installation and later reconfiguration costs. Furthermore, the above described systems may include specialized belt lengths that may be difficult to easily order in a standardized size or may be extremely difficult to repair. For example, if the elongated V-belt in FIG. 3 breaks, it is difficult to quickly and efficiently repair the system.